This is an issue that we are experiencing with my DP's daughter. She has always relied on her parents to play with her (although she does have older siblings), and was relying on me to do the same.
I recently told her and DP that I am happy to play minecraft, etc. with her, but that I can't spend my whole afternoon playing schools or mums & dads, as I have other things I need to get on with. DP has also decided to do the same thing.
We try to get her out to the park to play, but she definitely watches more YouTube that should be healthy.
What kind of toys does your DD have? Mine has dolls that she seems happy to play with on her own, to a degree, but when I suggested that she sets her teddies up as students and she is the teacher, she thought I was ridiculous!!
My own DM used to 'set up' the games for me, and that would help me to play on my own. For example, I loved my Sylvanian Families, so should would spend at most ten minutes setting up the characters, and I could basically continue with what she had created. May be worth a go.. xx